The present invention relates to pulsed or intermittently operated crossed-field devices such as magnetrons and crossed field amplifiers (CFAs). By way of example, U.S. Pat. No. 3,255,422 shows one such CFA device wherein a microwave entry waveguide provides radio frequency energy to an entry port for a slow wave propagating structure on an anode. A cathode is opposed to this anode across a gap. A solenoid maintains a magnetic field perpendicular to the applied electric field. The cathode is formed of a material having a secondary emission ratio greater than unity so that electrons emitted from the cathode due to the electric field follow re-entrant trajectories in the magnetic field and bombard the cathode to cause further electron emission. Energy exchange between the emitted electrons and the rf field results in amplification of the input signal, which is then coupled out at a microwave outlet port as an amplified signal.
Because the cathode is formed of a material selected to copiously emit secondary electrons, such devices, if not provided with a means for shutting down the electron emission, could continue to run spontaneously even when the input rf is removed. Thus, as set forth in the aforesaid U.S. Pat. No. 3,255,422, it is customary to provide a control electrode which during a turn-off phase is pulsed near anode potential to capture electrons and end the secondary electron re-emission. However, the control electrode requires a relatively high-powered pulse and high potential to dependably quench the electron flux. This may result in an inflexibility of operating characteristics, so that the device does not work dependably with power supplies or drivers having slightly different characteristics, or fails to shut down after hot, relatively long, operating cycles. Thus, for example, when used to amplify or supply high energy radar pulse sequences, shut down may become erratic when used with different models of power supply or pulse timing units.
Accordingly, it would be desirable to provide a crossed-field device having improved shut-down characteristics.
It would further be desirable to provide such a device wherein the control electrode operates at a lower potential or energy.